1. Field of the Invention
The invention pertains to the field of dental instruments. More particularly, the invention pertains to appliances which keep files and/or reamers from progressing too far into a root canal during treatment.
2. Description of Related Art
When a tooth experiences trauma including infection or a nerve in the root being adversely affected by proximity to a deeply set filling, the body (dental pulp) takes defensive measures to constrict the root canal to isolate it, or its defenses may be overcome by the irritant. If the diagnostic tests of the tooth reveal irreversible damage, a root canal or endodontic procedure is needed. A root canal treatment entails the removal of the central soft portion (nerves, blood vessels, tissues etc.) of the tooth. The empty space or canal is then filled with an inert material. The canal is sometimes too narrow and/or infected to effectively place the inert material inside it. Instruments, usually files and/or reamers, herein collectively termed xe2x80x9cfilesxe2x80x9d, are used to clean and/or widen this canal. Their mode of action while being used is either a push-pull or twisting motion.
In cleaning out the canal, it is important that the clinician not change the general shape of the canal, for example, by creating a ledge in it or by changing its curvature since if either of these events occur, there is an increased probability that one of the successively larger and stiffer files used to clean the canal will perforate the root wall. This in most cases requires surgical correction or extraction of the tooth. This complicates and prolongs the treatment, causing discomfort to patients.
In the preparation of root canals, it is the present practice to enter the chamber of the tooth with a file to enlarge the root canal. A plurality of endodontic files of increasing diameter are employed to enlarge the root canal to create a channel of size that can practically be filled with a medicament and then sealed. It is important in the preparation of the root canal to control the length of the file in order to limit the depth of penetration to avoid injury. The desired depth is called the working length.
The length of the tooth involved, as well as the length of the root canal, is determined by means of X-rays, and various techniques and devices have been devised in the past for limiting the depth of penetration of the root canal files to the root tip. Thus, many dentists employ a stop member which is penetrated by the root canal file for the desired distance, with the stop member being positioned to engage the top of the tooth to limit penetration.
However, these stop members, which are generally rubber stoppers, are easily displaced, particularly in working within the limited area of a patient""s mouth and considering the relatively small size of the instruments involved. There is nothing to stop the files from going too far into the canal.
It is difficult for the endodontist to precisely judge when the file has reached the end of the tooth. Additionally, the rubber stopper is both flexible and movable and can therefore allow the file to proceed deeper into the root canal then may be actually desired. In other instances, the inadequacies of the equipment result in incomplete penetration. Either too great or too shallow depth penetration could cause failure of the entire procedure. An additional problem is presented in that each individual file and its rubber stopper must be separately gauged against a separate scale or ruler and then individually set to the depth indicated in the x-ray. This procedure can involve inherent inaccuracies and a great deal of time and inconvenience to the dentist. Inaccuracies can also occur because of the number of manual operations involved. Further, problems relating to contamination of the file during this measurement or gauging procedure are likely to occur.
During an endodontic procedure, accuracy is compromised in both the determination of the working length, and maintaining this working length. In determining the working length, measuring any length requires two points. The first point that a dental practitioner uses is the tooth apex. The second is however an arbitrary point on the tooth that is lined up with a rubber stopper. Most times there is no clear reference point on the tooth that can be used repeatedly to get the same correct length. Either a different point is used or it is viewed at a different angle to get another measurement. It is very difficult to remember the reference points for each canal in multi-canal procedures. Some in the field say that practice and experience allows them to work around this problem. However, in reality, accuracy is not in the eye of the beholder.
When attempting to maintain the working length, assuming the accuracy of this length based on only one fixed point, the files are not effectively stopped from going too far into the canal. The point(s) chosen is not a platform that can support anything. The rubber stoppers do not provide any support if pressure is applied. During filing, the rubber stops give in a millimeter or two. Since in root canal treatment dentists generally go into the half-mm range, this reduces the accuracy of the whole procedure. A common defense to this problem is that the apical constriction stops the file. However, if this were the case, then there would be no reason to determine the length in the first place. Why not simply go ahead and file without finding the working length? In essence, this is currently what is being done since a working length is being determined and then can not be maintained.
It is almost impossible to move an unsupported object manually in one plane and keep it fixed in another plane. This principle is what root canal treatment has been based or more accurately not based upon for decades. Radiographs along with sophisticated and expensive instruments are used to determine the working length of the tooth. This length is indicated on the file. There is, however, no way to stop the file from overextending in the canal while it is being used.
Several prior art patents have tried to solve these problems.
U.S. Pat. No. 3,781,996, xe2x80x9cROOT CANAL REVERSIBLE STOP,xe2x80x9d Saffro (1974), shows an endodontic file with an intermediate part between a cutting portion and a handle which contains a series of reversible stop members. The fact that the stop is found on the instrument means that the point of measurement or reference changes with the movement or shifting of the instrument, hence it is impossible to get the same measurement twice. Since the essence of root canal treatment is to transfer measurement all the time, this system is not very accurate.
U.S. Pat. No. 3,838,517, xe2x80x9cCOMBINATION DEPTH STOP AND GAUGE ASSEMBLY FOR A DENTAL DRILLxe2x80x9d, Michnick (1974), is an assembly which attaches to a dental drill. The assembly includes a surface which controls the depth of the cut by the drill. The drill bit runs through this surface, and acts as a depth stop for the drill. The surface controls the depth of a cut, but the invention is not interested in working length, nor is it used for files. This mechanical and electrical device has stops that project between the device and the tooth limiting the extent to which the drill or instrument goes into the tooth. These stops work only with mechanical or electrical devices. They cannot currently be used for manual manipulation of the root canal since the stops are an integral part of the assembly of the device.
U.S. Pat. No. 3,961,422, xe2x80x9cSTOP DEVICE FOR ENDODONTIC INSTRUMENTS,xe2x80x9d Riitano et al. (1976), shows a stop for limiting the depth of penetration of an elongated dental instrument usable in an endodontic procedure. The stop is in the form of a disc divided into two halves. Manually assembling the two halves requires that they are big enough to handle with the fingers. If they were this big, then the assembled disc would be bulky and too large to work with in the confines of the mouth.
U.S. Pat. No. 4,028,810, xe2x80x9cROOT CANAL FILE,xe2x80x9d Vice (1977), is an endodontic instrument for treating a pulp canal which includes a handle portion adjustably mounted in telescoping relation on the shaft of an elongated working tool, with cooperating grooves in the shaft and handle preventing relative movement during use of the instrument. The working length of the tool projecting from the handle is adjusted and the tool and handle are interlocked. The end of the handle acts as a positive stop limiting the depth of penetration of the working tool portion during use of the instrument. The main disadvantage of this device is that it is tedious to change or adjust the stops since special tools are needed to do so. The fact that the stop is found on the instrument means that the point of measurement or reference changes with the movement or shifting of the instrument, hence it is impossible to get the same measurement twice. Since the essence of root canal treatment is to transfer measurement all the time, this system is not very accurate.
U.S. Pat. No. 4,165,562, xe2x80x9cPRECISION ENDODONTIC FILE,xe2x80x9d Sarfatti (1979) discloses an endodontic file with a threaded base and a threaded sleeve. The threaded sleeve receives the threaded base to facilitate adjustment of the file. The fact that the stop is found on the instrument means that the point of measurement or reference changes with the movement or shifting of the instrument, hence it is impossible to get the same measurement twice. Since the essence of root canal treatment is to transfer measurement all the time, this system is not very accurate.
U.S. Pat. No. 4,571,183, xe2x80x9cVIBRATORY ENDODONTIC DEVICE,xe2x80x9d Nash (1986), describes a vibratory endodontic device for mechanical preparation of dental radicular canals such as root canals, prior to their obturation. The device includes an endodontic file connected to a drive means for vibratory movement. This mechanical and electrical device has stops that project between the device and the tooth limiting the extent to which the drill or instrument goes into the tooth. These stops work only with mechanical or electrical devices. They cannot currently be used for manual manipulation of the root canal since the stops are an integral part of the assembly of the device.
U.S. Pat. No. 5,295,833, xe2x80x9cDENTAL ROOT CANAL DIAGNOSTIC AND TREATING EQUIPMENT,xe2x80x9d Chihiro (1994), teaches dental root canal diagnostic and treating equipment with specific positions, which serve as the reference positions. One of the reference positions to be set is the working length. This device electronically tells a dentist when the tip of the instrument reaches the tip of the root canal. It however does not or cannot transfer that measurement because it has no fixed precise location near the crown with which to repeat the measurement over and over again from the same points of reference.
U.S. Pat. No. RE35,147, xe2x80x9cDENTAL TOOL HOLDER,xe2x80x9d Apap et al. (1996), shows a dental tool holder for an endodontic filing tool in which the shaft of the worktool is held so as to be secured against rotational and axial movements. The worktool is set in motion with an exciter device having a component which is transverse relative to the axis of the worktool. A stop is guided in the housing of the handpiece with a rod containing teeth. This mechanical and electrical device has stops that project between the device and the tooth limiting the extent to which the drill or instrument goes into the tooth. These stops work only with mechanical or electrical devices. They cannot currently be used for manual manipulation of the root canal since the stops are an integral part of the assembly of the device.
U.S. Pat. No. 5,807,106 xe2x80x9cENDODONTIC INSTRUMENT HAVING DEPTH CALIBRATIONS AND METHOD OF FABRICATING SAME,xe2x80x9d Heath (1998), discloses a method of fabricating an endodontic instrument with depth indicating calibrations formed between the handle and the fluted tapered end portion. The calibrations are formed by a cold rolling operation. The device has no effective stop, but the grooves on the instrument will show up on the x-ray when the working length is being determined.
U.S. Pat. No. 5,915,964, xe2x80x9cFLEXIBLE GUIDED FILE FOR ROOT CANAL PROCEDURES,xe2x80x9d Walia (1999), uses a noncutting file guide at the tip of a flexible file. The guide is first inserted into the root canal, and the file is then moved along the guide. This patent states that the instrument should be inserted until it stops at the tip of the root but if this could be done with certainty then a file or reamer could be used to do this in the first place since this would be a natural stop. If the ball at the end of the instrument is small and passes through the root opening at the tip then there is nothing to stop the whole apparatus from passing through if there is no effective stop at the crown portion of the tooth.
Errors in depth penetration of the file into the root canal, either too deep or too shallow, are the major cause of failure in endodontic procedures. In seeking to overcome such failure, the prior art endodontic instruments have been largely unsuccessful because of complexity or impracticability. Further, none of the devices currently available offer any assurity of maintaining sterility. The stops on the mechanical devices cannot be used without the device themselves or with other mechanical devices or with manual manipulation. The devices that use screw-on stops need specialized files. Specialized stops are needed for many of the prior art devices. All of the devices with the stops on the instruments themselves rely on an arbitrary point of reference on the tooth that vary depending on the line of sight.
Therefore, there is a need in the art for improved accuracy of the root canal procedure. Specifically, a fixed platform from which to measure and maintain the working length is needed.
The appliance of the present invention works effectively during root canal treatment by being firmly attached to the tooth to be treated and having a fixed platform from which the file can have a fixed working length. The appliance has three functional parts: (1) an attachment section that is held against the tooth by a matrix retainer and band, (2) a resting section that rests against the occlusal or top of the crown of the tooth, and (3) a guide section with a hole that pivots or is fixed over the tooth. The appliance is preferably attached to the tooth by any tofflemiere type matrix holder and band. Once the working or desired length of the file is obtained, then it is placed into the guide section of the appliance which is stationary in one plane. Therefore, the file cannot extend further than the desired length into the canal. This appliance provides an effective stop for the file while it is being used.